Vacuum pump



April 2, 194s. GQ A. BECKER VACUUM PUMP Filed May 29, .1945

. INvEm-on y Ceor e A .B cker ATTORNEY Patented pr. 2, 1946 "UNITED STATES PATENT OFFICE VACUUM PUMP George A. Becker, San Bruno, Calif., assgnor lto Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Application May 29, 1943, Serial No. 489,251

(Cl. 23o-101) 10 Claims.

My invention relates to a vacuum pump of the oil diffusion type. l

It is among the objects of my invention to provide a simplified pump structure adapted to produce an exceptionally high vacuum with greater pumping speed and improved efficiency.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodiments thereof Within the scope of the claims.

Referring to the drawing, the single gure is a vertical vsectional View of the pump including the baille.

In terms of broad inclusion my diffusion pump comprises a tubular casing providing an upper pump chamber and a lower boiler chamber for the working fluid or oil. A vapor chimney is disposed in the pump chamber and is provided with -a plurality of umbrella-type jets; an improved arrangement and spacing of the jet hoods with respect to the casing being included. Improvements are also incorporated in the boiler structure, and in the sealing means at the base of the vapor chimney. Further improvements are provided in the vacuum connections to and baille arrangement for the pump.

I In greater detail, and referring to the drawing, the diffusion pump embodying my invention comprises a tubular casing 2 preferably of glass,

providing an upper pump chamber 3 and a lower boiler chamber 4 for the pump fluid or oil 6. A side arm or duct 'l is sealed to the casing adjacent the lower portions of pump chamber 3 for connection with a suitable backing pump. A mechanical pump capable of reducing `the fore pressure to say about .5 mm. or less may be used. To facilitate making connection with the backing pump, the side arm 'l is preferably bent upwardly and is provided with an outwardly extending elbow 9 having a flared enlargement for receiving a flanged coupling |2.

Oil 6 in the boiler chamber is heated by a resistance coil |3 held by a spiral glass core I4 having downturned `ends I5 sealed to the bottom of the casing. This core holds the heater in xed position spaced above the bottom. A pair of leads I6 are sealed to tubulations |'I on the sides of the boiler, to which leads the ends of the heater coil are connected. Glass beads |8 on the wire end leading to the center of the coil serve to insulate the parts.

The internal assembly of the pump is of metal,

such as spun aluminum, and includes a vapor chimney carrying a plurality of say three umbrella-type jets. From the structural standpoint the unit comprises a main chimney section I9 of substantially uniform diameter having an enlarged base 2|. Orices 22 of the lower jet are formed in the upper half of main chimney section I9, and ilaring hood 23 of this jet is supported by screws 24`threaded into the chimney.

Oriflces 26 of the intermediate jet are formed adjacent the top of the main vchimney section,

and flaring hood 2'|v of this jet is formed integrally with the reduced upper chimney section 28, the parts being secured by screws 29 threaded into the main chimney section. Orices 30 of the upper jet areformed adjacent the top of reduced chimney section 28.` `Flaring hood 25 of this jet is formed as a flangeon cap 3|, secured over the top by a screw 32. The internal pump assembly is centered by a three-armed spider 33 also held by screw V32.

Enlarged base 2| is preferablybell-shaped and seats on an annular shoulder 34 provided by a reduced neck formed in the casing betweenboiler chamber 4 and pump lchamber 3. The lower portions of 'the bell are preferably curved inwardly of the shoulder so that these parts form a snug fitting seat. This arrangement also centers the unit and supports it above the bottom of the,

boiler.r Oil condensing on theinner walls of the casing ilows downwardly and collects in a ring 36 above shoulder 34thereby forming a liquid seal at this joint. Suitable slots 3l in base 2| vprovide drain openings for returning excess oil from the pump chamber to the boiler, these openings being sized to maintain the desired amount of oil above the shoulder to preserve the liquid seal.

Connection with a manifold 38 communicating with the bulb to be evacuated is made by a coupling arrangement 39 which also preferably includes a baffle 40. The upper end of `casing 2 has a flared enlargement 4|, as has manifold 38, for receiving the halves of the coupling and associated gaskets 42. lMain bale 44|| and gasket rings 43 are clamped between the coupling sections, excessive lpressure on the gaskets being avoided and a resilient pressure maintained by springs 44 on coupling bolts 46. A secondary baille plate 4'| is mounted below aperture 48 by spacers 49. The underslung baille plate 4-1 shields the orifice and directs the incoming molecules laterally into the vapor stream issuing from the upper jet, which arrangement retardsbackstreaming into the manifold without unduly limiting admittance to the pump. v

In accordance with the usual operation of pumps of this kind, oil is evaporated in thel backing pump, the oil vapor condensing out along V the walls of the casing.

I have found it desirable to make the umbrella jets successively smaller in size as the jets approach the top of the chimney.V This decrease applies to both the size of the orifices a-nd to the deflecting hoods. As shown in the lower rimdiameter of hood 21 is smaller than that of hood 23; likewise the rim diameter of hood 25 is small-` er than that of hood 21. Consequently the clearance between the rims and the casing increases from jet to jet upwardly along the pump. I also prefer to restrict the diameter of the casing somewhat Ain the region surrounding the lower jet, this restriction extendingffrom about the upper end of hood 23 to the point where side arm 1 is con` nected.Y 'The cross-sectional area of the pumping chamber is thus greater inthe vicinity of the upper Vjets than at the lower jet.

With my pump, usinga -good grade of pump oil, it is possible'to produce at Vhigh pumping A speeds a low value of pressure, say of the order I claim: Y

k1j. A diusion pump comprising a tubular casing providing a lower boiler chamber and an upper pump chamber, said casing having a shoulder therein vrbetween said chambers, and a Vapor chimney in the pump chamber having its lower Vend seated on said shoulder, said end of the chimney being provided with an opening communicating between the boiler chamber and th'e pump chamber portions external the chimney.

2. A diffusion pump comprising a tubular cas-` ing providinga lower boiler chamber and an up Yper pump chamber, said Vcasing having'a shouly chambers, and a vapor chimney in the pump chamber having a lower endV shaped complementary to and seated on said shoulder, whereby oil condensing onthe casing collects to form a liquid seal at said shoulder, and a drain passage arranged to return excess oil to the boiler chamber.

4. A diffusion pump comprising a glass casing, a vapor chimney inY the casing, a duct sealed to a side of the casing adjacent the lower portions of said chimney, said duct having an enlarged outer end, and a sectional coupling having one halfengaging said enlarged end.

5. A diffusion pump comprising a casing having an enlarged upper end, a vapor chimney in the casing, a sectional coupling having one h'alf engaging said end, means clamping the coupling the casing, a sectional coupling having one half engaging said end, a gasket, interposed between said sections, bolts clamping the coupling secprising a main section having a bell-shaped lower end, an annular row of orices insaid section arranged intermediate the ends thereof, a hood on the section overlying said orifices, a second annular row of orices in vsaid section arranged adjacent the upper end thereof, la reduced upper chimney section having an enlarged lower end providing a h'ood for said second row of oriiices, said last mentioned section having-substantially straight vertical side walls extending upwardiy fromits enlarged end, another annular row of oriiicesl in said reduced section adjacent the upper end thereof, anda hood on the reduced section overlying` the last mentioned orifices.

Y 8.l A diffusion pump comprising a casing, a vapor chimney vin the casing, a duct registering with the upper end of th'e casing, a baiiie `above the chimney and interposed between said duct and casing, and'means Aclamping the duct and baiile and casing together.

9. A diiiusion pump comprising a casing providing an upper pump chamber and aiower boiler chamber for holdingza pumping fluid, a vapor chimney unit loosely disposed inthe pump `rcharnber with' its lower end communicating with the boiler chamber, said chimneyunit having .a spacer adjacent the upper end to hold it centered in the casing, said casing having an .opening at the top of greater width than said chimney unit whereby the latter is insertable through said opening, a duct communicating with the opening at `the top of said casing, means clamping the duct and cas-` ing together, and a heating element supported on the casing for boiling the fluid in said boiler chamber.

l0. A diffusion pump comprising va casing providing an upper pump chamber and a lower boiler chamber for holding a pumping uid, a vapor chimney unit loosely disposed in the pump chamber with its lower end communicatingrwith the Y boiler chamber, said chimney unit .having a spacer 

